Solid-state image sensors such as an MOS sensor and a charge-coupled device (CCD) are provided in digital cameras, mobile phones, and the like, and miniaturization of such sensors, and eventually pixels (cells) is required due to increased demand for high-definition imaging functions and smaller sizing.
FIG. 19 schematically shows a cross-section of a pixel part of a first type of conventional MOS sensor. Photoelectric conversion regions (photodiodes) 102 are formed in the surface of an Si substrate 101, and a wiring layer 104 is formed via an interlayer insulation film 103. Furthermore, a color filter 105 is formed above the interlayer insulator film 103 to allow light of a different color to enter each pixel. In addition, on-chip lenses 106 made from plastic for converging incident light to the photodiodes 102 are provided above the color filter 105. Although the miniaturization of the pixel (cell) itself is necessary in order to respond to the aforementioned requirement, light-collecting efficiency deteriorates with such miniaturization. This problem is caused by the fact that, when the cell size is reduced, the distance from the incidence surface of the on-chip lens 106 to the photoelectric conversion region (photodiode) 102 which is the actual light-receiving unit becomes longer than the focal point distance of the on-chip lens 106, and this focal point distance cannot be lengthened when the cell size is small, that is, light cannot be collected in the photodiode 102.
In order to address such a problem, the above-described first type has been modified into a second type of conventional technique which is provided with a region (hereafter called an optical waveguide region) having an optical waveguide function in which a high-refraction index region covered by a low-refraction index region is formed up to the vicinity of the upper surface of the photodiode and within a distance that allows light-collection by the on-chip lens (see Patent Literature 1). FIG. 20 schematically shows this second type of conventional technique. This second type of has the configuration of the first type of conventional technique shown in FIG. 19 as a basic pattern but includes, in the interlayer insulation film 103 below the color filter 105 and above the photodiodes 102, optical waveguide regions 301 made of a material (for example, SiN) having a higher refraction index than the interlayer insulation film (typically SiO2) 103. By adopting such a configuration, light incident on each of the optical waveguide region 301 is locked inside the optical waveguide region 301 and is wave-guided inside the optical waveguide region 301 to the corresponding photodiode 102. In other word, the light-collection loss due to the on-chip lens 106 having a short focal point distance is reduced. Furthermore, techniques of light-collecting in an optical waveguide region by shrinking the on-chip lens with respect to oblique incident light are disclosed.
Aside from the technique in Patent Literature 1 as described above, various techniques have been presented as the aforementioned second type of conventional technique.
Patent Literature 2 discloses a technique of forming an optical waveguide region on a charge-coupled device.
Patent Literature 3 discloses a technique which relates to the forming of an optical waveguide path in which the optical waveguide region has a 2-stage structure and a high-refraction index material is embedded in each of the stages.
Patent Literature 4 discloses a technique of increasing aperture ratio and improving the light-collecting efficiency for oblique incident light.